What are those spots on the leaves of my tomato plants?

I read about that tomato late blight but it doesn’t match what my tomato plants have. I have little brown freckles on the lowest leaves. Then, the leaf turns yellow and brown, gets crunchy and falls off. It’s moving up the plants. So what is it?

It’s our perennial favorite tomato disease in southern Michigan and it’s called Septoria Leaf Spot. Because last summer was pretty cold, we didn’t see much of it, just the Late Blight. With the warm, humid summer we are now having, Septoria is back and kickin’.

For people who have been spraying chlorothalonil every seven to ten days, they have repelled this fungus and virtually all fungal problems that tomatoes can get. This includes early blight, septoria leaf spot, anthracnose, late blight and fruit rot. This is one of the rare occasions where one fungicide fits all.

Keep in mind that all those brown, diseased leaves that fall onto the soil are next season’s starting Septoria team. And no, you can’t spray the soil and kill the fungus. All you can do is preventatively spray plants each season, beginning in early July. All fungicides protect but cannot cure the plant after the killer fungus invades.

Being a successful vegetable gardener now involves having just a touch of paranoia. You have to believe that evil, invisible Demon Dust is out there, floating about, searching out your plants.

When your use chlorothalonil to spray for Septoria and you already have it on the plant, there are still infected leaves on the tomato that are not showing symptoms. So for the next week or so, more leaves will get spotted and die. But these guys were infected long before the fungicide ever hit the leaves.

Keep in mind that overhead watering will wash the fungicide away. Because of the frequent rains, it is very important to reapply fungicide as soon as possible after the plant has dried off. Time to step up to the plate. Either spray with chlorothalonil now to protect your tomatoes or accept the fact that you may have to buy those red orbs from someone else.

This is about the fourth or fifth year that my large maples have gotten these big, grotesque black spots on their leaves in the middle of the summer. It looks so bad and I know the trees are suffering. What is causing this and how do I prevent it?

Keep in mind that you and the maples are two separate life forms. You are distressed. The trees are not. This is a common fungal problem called Tar Spot.

The only trees that are affected are maples and occasionally boxelder because they belong to the same Acer family. Japanese maples have the “get out of jail free” pass on tar spot. The fungus gets into the leaves very early in the season.

In June or July, little, yellowed spots develop and then the spots become black, shiny and coalesce. Often, the black spot has a yellow ring around it. This is a cosmetic disease. It affects leaf appearance but not tree health.

You may be able to limit the return of tar spot next year by picking up and destroying fallen maple leaves. But consider that none of your neighbors are doing the same.

— Gretchen Voyle is the horticulture educator for the MSU Extension-Livingston County. You can reach her with your questions and comments by calling (517) 546-3950.

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